Medicinal inhalers can deliver a medicine or drug to the circulatory system of a patient more rapidly than ingestion (e.g. swallowing a pill) or subcutaneous injection (SCI), but typically less rapidly than intravenous injection. Medicinal inhalers are especially rapid in delivering medicines to a patient's lungs, heart, or central nervous system because blood flow from the lungs proceeds directly to the heart and from there to the brain. Moreover, the use of a medicinal inhaler is typically painless and much more convenient (for the patient) than is SCI or intravenous injection, and may reduce the risk of infection and eliminate the risks associated with improper needle disposal. For at least these reasons, inhalation has become a preferred method for patients to self-introduce certain medicines, for example bronchodilators and various psychoactive drugs.
There are several broad types of medicinal inhalers, each type distinguishable from the others by its structural and functional characteristics and by a different set of advantages and disadvantages.
So-called “atomizer” type inhalers disperse liquid particles into an inhaled gas such as air. The inhaled medicine is carried within the liquid, for example the medicine may be in solution with the liquid. Such a delivery method can be suitable for certain medicines that are adequately stable in the liquid, for example medicines that can maintain efficacy in the liquid over long periods. However, many medicines are unsuitable for long term storage in liquid form.
So-called “dry powder” type inhalers are configured to disperse dry solid particles of a medicine into an inhaled gas. Dry powder inhalers have the advantage that the medicine is stored in dry solid form and therefore may retain its efficacy longer. However, the solid particles can be relatively large or irregular in size and shape, adversely affecting the uniformity and depth of drug distribution within the lungs and/or potentially irritating the lungs of the inhaling patient.
So-called “vaporizing” inhalers utilize a heat source to cause rapid sublimation, and/or melting followed by evaporation, of a solid medicine into gaseous form. An example of a vaporizing inhaler is described in U.S. Patent Publication No. 2005/0268911A1 to Cross et al. The patient typically inhales the heated medicinal gas after it is mixed with a cooler diluting gas such as air. Vaporizing inhalers have the advantage that the medicine is stored in solid form (i.e. potentially maintaining efficacy over a longer period of storage) and the inhaled gas is less likely to irritate the lungs of the inhaling patient because the inhaled gas does not include an excessive size or number of solid particles. However, because vaporizing inhalers typically require a rapid but well-controlled temperature rise in the solid medicine, the design of a practical, safe, and low-cost vaporizing inhalers can be a formidable challenge.
Thus, there is a need in the art for an improved vaporizing inhaler design that is suitable for safe and practical use while also being suitable for high-volume manufacture at acceptably low cost.